Mold dressing



V 2.95am Patented Oct. 18, 1960 Free NIOLD DRESSING John M. Casteras, 'Colonia, N..l., assignor to International Smelting and Refining Company, a corporation of Montana No Drawing. Filed Mar. 12, 1957, Ser. No. 645,400

Claims. (Cl. 106-3822) This invention relates to mold dressings for coating the molding surface of a mold for molten metal and, more particularly, to an improved mold dressing comprising a dispersion of finely comminuted carbon, especially boneblack and graphite, in a petroleum oil containing a small amount of lecithin.

It is well known that if copper shapes are cast by pouring the molten metal into a dry copper mold, the surface of the resultant casting is generally pitted and otherwise marked by imperfections which render it unsuitable for working into wrought copper shapes. Accordingly it has long been standard practice to apply a mold dressing to the molding surface of the mold immediately prior to pouring the molten metal into the mold. A mold dressing which effectively coats the entire molding surface of the mold not only imparts a smooth, pitfree surface to the casting, but also is effective for preventing the casting from sticking in the mold.

A particularly successful mold dressing is one which comprises a dispersion of finely comminuted carbon, such as graphite and boneblack, in a petroleum oil vehicle. However, the quality of the mold dressing is greatly affected by minor variations in the quality of the oil. The source of the crude, the proportion of light to heavy fractions, and other factors which have not as yet been identified, all affect the suitability of the oil as a mold dressing vehicle. As a result the preparation of an effective mold dressing is an art which depends on securing a light petroleum which experience shows to be satisfactory.

The present invention is based on the discovery that light petroleum fuel oils which alone are unsuitable for use as a mold wash vehicle can be made suitable, and that even the most satisfactory oils for such use can be improved, by incorporating a small amount of lecithin in the oil. The mold dressing of this invention therefore comprises a light hydrocarbon oil containing approximately 0.1 to 2.0% by weight of lecithin, in which there is dispersed approximately 1 to pounds of finely comminuted carbon per gallon of oil.

The light hydrocarbon oil preferably is a petroleum oil meeting substantially the specifications of commercial Number 2 light fuel oil, and it may with advantage have blended therewith a minor proportion (say about 20% by volume) of a relatively heavy petroleum residuum. Except for the fact that a mold dressing according to this invention is much less sensitive to minor variations in the source and proportion of the oil than has been the case heretofore, the oil used is of the same character as has been employed in heretofore known mold dressings.

The finely comminuted carbon is any of the commercial carbons, such as boneblack, boneash, or graphite, that has heretofore been employed in mold dressings, and the amount used is the same as has been conventional. A

particularly satisfactory carbon mixture is composed of about equal parts by weight of boneblack and graphite.

It is the addition of the lecithin which makes it possible to use a wide range of inexpensive fuel oils and blends as the mold dressing vehicle. Any commercially available lecithin may be used. Soya lecithin, which is recovered from soy beans, is inexpensive and very satisfactory. The amount of lecithin required is small. Generally it is in the above stated range from 0.1 to 2.0% by weight of oil; but it is more generally below 1.0% than above. A preferred concentration range is from 0.25 to 1.5% of lecithin by weight of the oil vehicle.

When preparing the new mold dressing, the carbon and oil are mixed together in the usual manner and the full amount of lecithin may be simply stirred into the mixture. It is not necessary to pre-mix or pre-melt the lecithin with a small amount of the oil or of the carbon mixture since the lecithin readily dissolves and disperses in the composition.

Following is an example of the mold dressing of this invention:

To 10 gallons of a commercial Number 2 fuel oil was added 25 pounds of finely comminuted commercial graphite and 22 pounds of commercial boneblack. An amount of commercial refined soya lecithin, equivalent to about 1.0% by weight of the oil was then introduced and the mixture was agitated until the lecithin had dissolved. The resulting product was used as a mold dressing in molds for casting three inch diameter phosphorusdeoxidized copper billets. it was noted that the film of dressing on the molds was smooth and continuous, and free from sagging. Separation of vehicle from the carbon solids was substantially eliminated and the gloss or sheen of the film was greatly improved. As a result of these characteristics, copper billets cast in the molds which had been coated with this dressing were consistently of excellent quality. Indeed, experimental use of this new mold dressing on a substantial scale has resulted in fewer than /2 of 1% rejections on account of surface imperfections.

I claim:

1. A mold dressing for coating the molding surface of a mold for molten metal consisting essentially of a light hydrocarbon oil which contains approximately 0.1 to 2.0 percent by weight of a lecithin and in which there is dispersed approximately 1 to 10 pounds of a finely comminuted carbon per gallon of oil.

2. A mold dressing for coating the molding surface of a mold for molten metal consistin essentially of a light hydrocarbon oil which contains approximately 0.1 to 2.0 percent by weight of a lecithin and in which there is dispersed approximately 1 to 10 pounds of a finely comminuted mixture of boneblack and graphite per gallon of oil.

3. A mold dressing for coating the molding surface of a mold for molten metal consisting essentially of a light hydrocarbon oil which contains approximately 0.25 to 1.5 percent by weight of a lecithin and in which there is dispersed approximately 1 to 10 pounds of a finely comminuted carbon per gallon of oil.

4. A mold dressing for coating the molding surface of a mold for molten metal consisting essentially of a light hydrocarbon oil which contains approximately 0.25 to 1.5 percent by weight of a lecithin and in which there is dispersed 1 to 10 pounds of a finely comminuted mixture of boneblack and graphite per gallon of oil.

5. A mold dressin for coating the molding surface of 3 4 a mold for molten metal consisting essentially of a light 2,649,381 Hempel et al. Aug. 18, 1953 petroleum fuel oil which contains approximately 0.25 to 2,688,001 Echols Aug. 31, 1954 1.5 percent by Weight of a soya lecithin and in which there is dispersed approximately 1 to 10 pounds of a FOREIGN PATENTS finely comminuted substantially evenly proportioned mix- 5 698,483 Great Britain Oct 14, 1953 ture of boneblack and graphite per gallon of oil.

OTHER REFERENCES References Clted m'the file of thls patent Schwartz-Perry Surface Active Agents, pub. 1949 UNITED STATES PATENTS 10 (pages 486 and 487), Interscience Pub. Inc., N.Y. 2,257,601 Hall et a1. Sept. 30, 1941 Condensed Chemical Dictionary-Published by Rein- 2,618,032 Traenkner Nov. 18, 1952 hold (4th ed.) (page 395 relied upon). 

1. A MOLD DRESSING FOR COATING THE MOLDING SURFACE OF A MOLD FOR MOLTEN METAL CONSISTING ESSENTIALLY OF A LIGHT HYDROCARBON OIL WHICH CONTAINS APPROXIMATELY 0.1 TO 2.0 PERCENT BY WEIGHT OF A LECITHIN AND IN WHICH THERE IS DISPERSED APPROXIMATELY 1 TO 10 POUNDS OF A FINELY COMMINUTED CARBON PER GALLON OF OIL. 